Summary: metabolic disorders, such as obesity and sarcopenia, may result from disturbances in human energy balance caused by malfunctioning endocrine organs. To diagnose and monitor these conditions, analyzing body composition (BC) is crucial. Ultrasonography (US) is a cost-effective, non-invasive method widely used to study BC by directly measuring fat tissues, muscles, and organs in different body regions. This review focuses on exploring the clinical significance of US in assessing BC, especially in abdominal fat compartments, subcutaneous adipose tissue, skeletal muscle, and liver.
Key Points: BC, ultrasound, techniques, metabolic disorders, tissue analysis, muscles, abdomen, liver, standardization
Original submission date: Dec 14, 2019. Accepted for publication: May 07, 2020.
In addition to the physical impacts of metabolic disorders, there are also significant psychological and emotional effects. Individuals with obesity or sarcopenia may experience lowered self-esteem, depression, and anxiety due to societal stigma and health concerns. It is important for healthcare providers to address these holistic aspects of metabolic disorders in order to provide comprehensive care.
Research on potential treatments for metabolic disorders is ongoing, with a focus on lifestyle interventions, pharmacological therapies, and surgical options. The development of personalized medicine approaches based on individual metabolic profiles shows promise in improving outcomes for individuals with these conditions.
Educating the public on the importance of maintaining a healthy lifestyle, including regular exercise and a balanced diet, is key in preventing metabolic disorders. Early detection and intervention can help mitigate the long-term health consequences associated with obesity and sarcopenia.
In conclusion, understanding the impact of energy control on metabolic disorders is essential in addressing the global health burden of obesity and sarcopenia. Further research and advancements in treatment strategies are needed to improve outcomes and quality of life for individuals affected by these conditions.
The Limitations of Using Body Mass Index for Obesity Assessment
While BMI is a common metric for evaluating obesity by calculating weight-to-height ratio, it cannot differentiate between fat mass and lean mass. This limitation results in an inaccurate assessment of BC, particularly overestimating fat in individuals with higher muscle mass without providing insights into fat distribution.
Waist circumference is frequently used to measure abdominal fat but is unable to distinguish between visceral and subcutaneous fat, leading to unreliable correlations with cardiovascular risk. Different population groups have proposed various cut-off points for waist circumference measurements to account for height-related metabolic risks.
Ultrasound Evaluation of Abdominal Adiposity
Since the 1990s, ultrasound has been utilized to assess abdominal fat, particularly measuring visceral adiposity. Visceral fat parameters are commonly measured with an ultrasound probe on the abdomen while the subject is in a supine position and the abdomen is at a normal exhalation. Skill and training are crucial for accurate results, as factors like obesity and fasting can impact measurement precision.
There are several approaches to assess abdominal adiposity using ultrasound, with different measures focusing on visceral fat like intra-abdominal fat thickness (IAFT) and mesenteric fat thickness (MFT).
Intra-abdominal fat thickness (IAFT)
IAFT, a significant measurement in ultrasound adiposity assessment, is typically evaluated using a convex probe. Various anatomical references are used to determine IAFT, such as distances between specific structures in the abdomen.
Figure 1: Illustration of abdominal sagittal and axial sections where ultrasound measures are taken.
Figure 2: Anatomical positioning of the ultrasound probe for IAFT and MFT evaluation.
Mesenteric fat thickness (MFT)
MFT measurement involves using a convex ultrasound probe around the umbilical region to determine the distance between mesenteric surfaces.
Pre-peritoneal fat thickness (PFT)
PFT, as part of the abdominal wall fat index (WFI), is measured with specific ultrasound probes below the xiphoid process along the xiphoumbilical line.
Figure 3: Illustration and anatomical postures of ultrasound probes for subcutaneous fat and PFT evaluation.
Figure 4: Anatomical postures while evaluating subcutaneous tissue thickness.
These measurements provide valuable insights into visceral fat levels and potential health risks associated with fat distribution patterns.
Abdominal WFI
The abdominal wall fat index is a helpful measure to assess regional fat distribution, aiding in the classification of obesity types based on visceral or subcutaneous fat ratios.
Epicardial fat
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Epicardial fat, a visceral fat depot near the heart, is assessed using ultrasound in specific positions for precise evaluation of health risks associated with its thickness.
Peri- and para-renal fat
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Adipose tissues around the kidneys, termed peri-renal and para-renal fat, are crucial indicators of metabolic health and cardiovascular risk, measured using ultrasound techniques.
The Significance of Visceral Adipose Tissue in Metabolic Disorders
Visceral adipose tissue, located in the abdomen and thorax, is considered the most hazardous fat type due to its association with insulin resistance, dyslipidemia, and other predictors of cardiovascular risk. Ultrasound-assessed visceral adiposity correlates strongly with various clinical and laboratory markers, highlighting its importance in understanding metabolic disorders.
Studies have shown a positive relationship between mesenteric fat thickness and metabolic parameters, underscoring the role of ultrasound in assessing visceral adiposity and its implications on health outcomes.
The level of epicardial adipose tissue, which is significantly higher in individuals with metabolic syndrome (MS) compared to those without MS, is directly linked to LDL cholesterol levels and is also associated with blood pressure, fasting glucose, inflammatory markers. Conversely, it is inversely related to insulin sensitivity.
In a recent study by Bertoli et al., VAT was found to be strongly and independently associated with MS and its components, showing a stronger correlation than WC with high liver enzyme values and similar association with high uric acid levels. The study also concluded that VAT correlates better or equally to clinical parameters compared to WC, except for high blood pressure and low HDL cholesterol levels.
Additionally, the research by Bellan et al. highlighted a strong association between VAT, BMI, and WC across various BMI categories. The study suggested that incorporating VAT measurements by ultrasound into predictive models could enhance the accuracy of assessing cardiovascular risk factors.
Moreover, Jena et al. discovered higher VAT thickness in women with polycystic ovary syndrome (PCOS) compared to healthy controls, indicating a significant correlation with various cardiovascular risk factors.
Thaware et al. observed that measuring VAT in early pregnancy independently predicts the risk of gestational diabetes mellitus (GDM), suggesting its potential use in selective screening for GDM.
Various studies have shown a consistent relationship between US-assessed VAT measurements and metabolic and cardiovascular parameters, emphasizing the role of visceral abdominal fat in cardiometabolic risk factors.
Despite some limitations, ultrasound has the potential to become a valuable tool in evaluating body composition and managing metabolic diseases.
Patients with specific conditions, such as lipodystrophy, prefer more accurate imaging methods like MRI, CT, and DXA. Ultrasound should be used cautiously for more precise fat distribution measurements, as it depends more on the operator compared to other methods. Developing a standardized protocol for assessing body composition parameters using ultrasound is necessary to minimize errors.
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Footnote
This article has undergone external peer review and was commissioned by the journal editorial board. All authors have declared no conflicts of interest. Despite the promise, ultrasound still faces challenges in body composition assessment, requiring further research for successful implementation in clinical practice.
In addition to the references provided, ultrasound imaging has emerged as a valuable tool for evaluating body composition. It can be used to assess various aspects such as fat distribution, muscle mass, and even organ health.
Ultrasound scans can help in the assessment of metabolic syndrome and blood pressure, as well as in understanding the association between fat deposits and cognitive decline in the elderly. Moreover, ultrasound can also reveal correlations between fat thickness and heart problems, diabetes, and atherosclerosis.
Furthermore, ultrasound imaging plays a crucial role in measuring muscle thickness and quality. It can help in diagnosing conditions like sarcopenia and assessing muscle strength in individuals, especially the elderly. Additionally, ultrasound can be used to predict total and regional skeletal muscle mass, providing valuable information for assessing physical performance and potential indications of sarcopenia.
Overall, ultrasound imaging offers a non-invasive and reliable method for evaluating body composition, diagnosing various health conditions, and monitoring changes over time. The information obtained from ultrasound scans can be crucial for developing personalized treatment plans and interventions for individuals at risk of or already affected by obesity, metabolic disorders, and muscle-related conditions.
Reference:
Ponti F, De Cinque A, Fazio N, Napoli A, Guglielmi G, Bazzocchi A. Ultrasound imaging, a tool for evaluating body composition. Available in Quant Imaging Med Surg 2020;10(8):1699-1722. doi: 10.21037/qims-19-1048